When corrugated boxes and polyolefin bags are stacked on pallets, it is desirable that these boxes or bags remain in a stable group, or unitized. This is particularly important for warehousing operations. Large numbers of boxes or bags are piled on wooden pallets and moved from place to place on forklifts. The pallets may be raised on elevators for warehouse storage or for long-distance transport. When the stored item is actually used, a single box or bag may be picked up and carried, for example, by a plant operator. Various devices are used to unitize pallet loads, including plastic straps, glues, hot melt adhesives and stretch wrapped films.
Now there is a simple, economical way to securely unitize pallet loads of synthetic polymer or polymer-coated packages that reduces or eliminates the need for stretch-wrapped films and also avoids the residue and surface damage caused by glues and hot melt adhesives. A water-based bonding agent can be manually or automatically sprayed on packages as they move along a conveyor. The bonding agent begins working virtually immediately as containers are stacked on the pallet, forming a tight, no-slip bond that prevents the load from shifting during warehouse handling or distribution.
When depalletized, the packages separate easily, without tearing or defacing the outer surfaces. The bonding agent is also preferably for single use. Once the packages are separated, they do not re-bond to one another.
The bonding agent is clear on drying, nontoxic, nonflammable, and is aqueous based instead of relying on volatile organic solvents. It is virtually invisible when containers are separated, leaving no sticky residue. It does not interfere with readings taken by automatic scanners, and does not affect the recyclability of synthetic polymer packaging.
Various types of materials are known which can be applied to different types of packages to stabilize palletized containers.
For example, in U.S. Pat. No. 3,734,801, issued to Sebel on May 22, 1973 relates to an aqueous colloidal adhesive made of xanthan gum and possibly other additives such as polyvinyl methyl ether and finely divided silicic acid. This material is disclosed to be useful with paper, cardboard, or pasteboard.
Palletizing aids are known for use with fibrous or cardboard containers, as seen, for example, in U.S. Pat. Nos. 4,148,111 and 4,452,723 issued Nov. 29, 1983 and Jun. 5, 1984 respectively to Carstens, which relate to a non-skid composition made of an aqueous suspension of colloidal silica and urea.
Palletizing adhesives are known for use with polyolefin packaging and polymer or wax-coated boxes, but many of the known materials, such as those disclosed in European patent publication EP 278 888, are based on organic solvents, which often present environmental difficulties. As a result, stretch-wrapped film is typically used for palletizing polyolefin packages.
A reusable adhesive coating for pallets supporting oily or lubricated articles is disclosed in German patent publication DE 3101812 A1. This coating contains permanent pressure sensitive adhesives and silanes, (page 1 of translation) and has a drying time of 2-3 days (page 13, last line, to page 14, line 1). It is applied to "pallets" that transport single workpieces between workstations (page 5, lines 1-18). These pallets are specifically adapted for use with handling robots, and are intended to be re-usable (page 6, lines 16-19).